Comparative genomic mapping of uncharacterized canine retinal ESTs to identify novel candidate genes for hereditary retinal disorders

PURPOSE

To identify the genomic location of previously uncharacterized canine retina-expressed expressed sequence tags (ESTs), and thus identify potential candidate genes for heritable retinal disorders.

METHODS

A set of over 500 retinal canine ESTs were mapped onto the canine genome using the RHDF(5000-2) radiation hybrid (RH) panel, and the resulting map positions were compared to their respective localization in the CanFam2 assembly of the canine genome sequence.

RESULTS

Unique map positions could be assigned for 99% of the mapped clones, of which only 29% showed significant homology to known RefSeq sequences. A comparison between RH map and sequence assembly indicated some areas of discrepancy. Retinal expressed genes were not concentrated in particular areas of the canine genome, and also were located on the canine Y chromosome (CFAY). Several of the EST clones were located within areas of conserved synteny to human retinal disease loci.

CONCLUSIONS

RH mapping of canine retinal ESTs provides insight into the location of potential candidate genes for hereditary retinal disorders, and, by comparison with the assembled canine genome sequence, highlights inconsistencies with the current assembly. Regions of conserved synteny between the canine and the human genomes allow this information to be extrapolated to identify potential positional candidate genes for mapped human retinal disorders. Furthermore, these ESTs can help identify novel or uncharacterized genes of significance for better understanding of retinal morphology, physiology, and pathology.

The dog genome

Over the last few centuries, several hundred dog breeds have been artificially selected through intense breeding, resulting in the modern dog population having the widest polymorphism spectrum in terms of body shape, behavior and aptitude among mammals. Unfortunately, this diversification has predisposed most breeds to specific diseases of genetic origin. The highly fragmented nature of the dog population offers a great opportunity to track the genes and alleles responsible for these diseases as well as for the various phenotypic traits. This has led to a thorough analysis of the dog genome. Here, we report the main results obtained during the last ten years, culminating in the recent publication of a complete dog genome sequence.

A comparative genome approach to marker ordering

MOTIVATION

Genome maps are fundamental to the study of an organism and essential in the process of genome sequencing which in turn provides the ultimate map of the genome. The increased number of genomes being sequenced offers new opportunities for the mapping of closely related organisms. We propose here an algorithmic formalization of a genome comparison approach to marker ordering.

RESULTS

In order to integrate a comparative mapping approach in the algorithmic process of map construction and selection, we propose to extend the usual statistical model describing the experimental data, here radiation hybrids (RH) data, in a statistical framework that models additionally the evolutionary relationships between a proposed map and a reference map: an existing map of the corresponding orthologous genes or markers in a closely related organism. This has concretely the effect of exploiting, in the process of map selection, the information of marker adjacencies in the related genome when the information provided by the experimental data is not conclusive for the purpose of ordering. In order to compute efficiently the map, we proceed to a reduction of the maximum likelihood estimation to the Traveling Salesman Problem. Experiments on simulated RH datasets as well as on a real RH dataset from the canine RH project show that maps produced using the likelihood defined by the new model are significantly better than maps built using the traditional RH model.

AVAILABILITY

The comparative mapping approach is available in the last version of de Givry,S. et al. [(2004) Bioinformatics, 21, 1703-1704, www.inra.fr/mia/T/CarthaGene], a free (the LKH part is free for academic use only) mapping software in C++, including LKH (Helsgaun,K. (2000) Eur. J. Oper. Res., 126, 106-130, www.dat.ruc.dk/keld/research/LKH) for maximum likelihood computation.

A canine cancer-gene microarray for CGH analysis of tumors

As with many human cancers, canine tumors demonstrate recurrent chromosome aberrations. A detailed knowledge of such aberrations may facilitate diagnosis, prognosis and the selection of appropriate therapy. Following recent advances made in human genomics, we are developing a DNA microarray for the domestic dog, to be used in the detection and characterization of copy number changes in canine tumors. As a proof of principle, we have developed a small-scale microarray comprising 87 canine BAC clones. The array is composed of 26 clones selected from a panel of 24 canine cancer genes, representing 18 chromosomes, and an additional set of clones representing dog chromosomes 11, 13, 14 and 31. These chromosomes were shown previously to be commonly aberrant in canine multicentric malignant lymphoma. Clones representing the sex chromosomes were also included. We outline the principles of canine microarray development, and present data obtained from microarray analysis of three canine lymphoma cases previously characterized using conventional cytogenetic techniques.

Detailed four-way comparative mapping and gene order analysis of the canine ctvm locus reveals evolutionary chromosome rearrangements

Canine tricuspid valve malformation (CTVM) maps to canine chromosome 9 (CFA9), in a region syntenic with gene-dense human chromosome 17q. To define synteny blocks, we analyzed 148 markers on CFA9 using radiation hybrid mapping and established a four-way comparative map for human, mouse, rat, and dog. We identified a large number of rearrangements, allowing us to reconstruct the evolutionary history of individual synteny blocks and large chromosomal segments. A most parsimonious rearrangement scenario for all four species reveals that human chromosome 17q differs from CFA9 and the syntenic rodent chromosomes through two macroreversals of 9.2 and 23 Mb. Compared to a recovered ancestral gene order, CFA9 has undergone 11 reversals of <3 Mb and 2 reversals of >3 Mb. Interspecies reuse of breakpoints for micro- and macrorearrangements was observed. Gene order and content of the ctvm interval are best extrapolated from murine data, showing that multispecies genome rearrangement scenarios contribute to identifying gene content in canine mapping studies.

Chromosome aberrations in canine multicentric lymphomas detected with comparative genomic hybridisation and a panel of single locus probes

Recurrent chromosome aberrations are frequently observed in human neoplastic cells and often correlate with other clinical and histopathological parameters of a given tumour type. The clinical presentation, histology and biology of many canine cancers closely parallels those of human malignancies. Since humans and dogs demonstrate extensive genome homology and share the same environment, it is expected that many canine cancers will also be associated with recurrent chromosome aberrations. To investigate this, we have performed molecular cytogenetic analyses on 25 cases of canine multicentric lymphoma. Comparative genomic hybridisation analysis demonstrated between one and 12 separate regions of chromosomal gain or loss within each case, involving 32 of the 38 canine autosomes. Genomic gains were almost twice as common as losses. Gain of dog chromosome (CFA) 13 was the most common aberration observed (12 of 25 cases), followed by gain of CFA 31 (eight cases) and loss of CFA 14 (five cases). Cytogenetic and histopathological data for each case are presented, and cytogenetic similarities with human non-Hodgkin's lymphoma are discussed. We have also assembled a panel of 41 canine chromosome-specific BAC probes that may be used for accurate and efficient chromosome identification in future studies of this nature.

Comparison of MultiMap and TSP/CONCORDE for constructing radiation hybrid maps

Radiation hybrid (RH) map construction allows investigators to locate both type I and type II markers on a given genome map. The process is composed of two steps. The first consists of determining the pattern distribution of a set of markers within the different cell lines of an RH panel. This is mainly done by polymerase chain reaction (PCR) amplification and gel electrophoresis, and results in a series of numbers indicating the presence or the absence of each marker in each cell line. The second step consists of a comparison of these numbers, using various algorithms, to group and then order markers. Because different algorithms may provide (slightly) different orders, we have compared the merits of the MultiMap and TSP/CONCORDE packages using a data set of information currently under analysis for construction of the canine genome RH map.

Structure, chromosomal location, and analysis of the canine Cu/Zn superoxide dismutase (SOD1) gene

Mutations in Cu/Zn superoxide dismutase (SOD1), a major cytosolic antioxidant enzyme in eukaryotic cells, have been reported in approximately 20% of familial amyotrophic lateral sclerosis (FALS) patients. Hereditary canine spinal muscular atrophy (HCSMA), a fatal inherited motor neuron disease in Brittany spaniels, shares many clinical and pathological features with human motor neuron disease, including FALS. The SOD1 coding region has been sequenced and cloned from several animal species, but not from the dog. We have mapped the chromosomal location, sequenced, and characterized the canine SOD1 gene. Extending this analysis, we have evaluated SOD1 as a candidate for HCSMA. The 462 bp SOD1 coding region in the dog encodes 153 amino acid residues and exhibits more than 83% and 79% sequence identity to other mammalian homologues at both the nucleotide and amino acid levels, respectively. The canine SOD1 gene maps to CFA31 close to syntenic group 13 on the radiation hybrid (RH) map in the vicinity of sodium myo/inositol transporter (SMIT) gene. The human orthologous SOD1 and SMIT genes have been localized on HSA 21q22.1 and HSA 21q21, respectively, confirming the conservation of synteny between dog syntenic group 13 and HSA 21. Direct sequencing of SOD1 cDNA from six dogs with HCSMA revealed no mutations. Northern analysis indicated no differences in steady-state levels of SOD1 mRNA.

The genome sequence of Schizosaccharomyces pombe

We have sequenced and annotated the genome of fission yeast (Schizosaccharomyces pombe), which contains the smallest number of protein-coding genes yet recorded for a eukaryote: 4,824. The centromeres are between 35 and 110 kilobases (kb) and contain related repeats including a highly conserved 1.8-kb element. Regions upstream of genes are longer than in budding yeast (Saccharomyces cerevisiae), possibly reflecting more-extended control regions. Some 43% of the genes contain introns, of which there are 4,730. Fifty genes have significant similarity with human disease genes; half of these are cancer related. We identify highly conserved genes important for eukaryotic cell organization including those required for the cytoskeleton, compartmentation, cell-cycle control, proteolysis, protein phosphorylation and RNA splicing. These genes may have originated with the appearance of eukaryotic life. Few similarly conserved genes that are important for multicellular organization were identified, suggesting that the transition from prokaryotes to eukaryotes required more new genes than did the transition from unicellular to multicellular organization.

Chromosome-specific single-locus FISH probes allow anchorage of an 1800-marker integrated radiation-hybrid/linkage map of the domestic dog genome to all chromosomes

We present here the first fully integrated, comprehensive map of the canine genome, incorporating detailed cytogenetic, radiation hybrid (RH), and meiotic information. We have mapped a collection of 266 chromosome-specific cosmid clones, each containing a microsatellite marker, to all 38 canine autosomes by fluorescence in situ hybridization (FISH). A 1500-marker RH map, comprising 1078 microsatellites, 320 dog gene markers, and 102 chromosome-specific markers, has been constructed using the RHDF5000-2 whole-genome radiation hybrid panel. Meiotic linkage analysis was performed, with at least one microsatellite marker from each dog autosome on a panel of reference families, allowing one meiotic linkage group to be anchored to all 38 dog autosomes. We present a karyotype in which each chromosome is identified by one meiotic linkage group and one or more RH groups. This updated integrated map, containing a total of 1800 markers, covers >90% of the dog genome. Positional selection of anchor clones enabled us, for the first time, to orientate nearly all of the integrated groups on each chromosome and to evaluate the extent of individual chromosome coverage in the integrated genome map. Finally, the inclusion of 320 dog genes into this integrated map enhances existing comparative mapping data between human and dog, and the 1000 mapped microsatellite markers constitute an invaluable tool with which to perform genome scanning studies on pedigrees of interest.

DNA sequence and physical mapping of the canine transglutaminase 1 gene

The transglutaminase 1 gene (TGM1) encodes an enzyme necessary for cross-linking the structural proteins that form the cornified envelope, an essential component of the outermost layer of the skin, the stratum corneum. Reported here is the complete coding region of canine TGM1, its chromosome localization, and its map position in the integrated canine linkage-radiation hybrid map. Canine TGM1 consists of 2,448 nucleotides distributed over 15 exons. The nucleotide sequence has 90% identity to human TGM1. The deduced canine TGM1 protein is 816 amino acids long and is 92% identical to human TGM1. Using fluorescence in situ hybridization, we localized canine TGM1 to dog (Canis familiaris) chromosome 8 (CFA 8q). Canine TGM1 localized to CFA 8 on the integrated linkage-radiation hybrid map in the interval FH2149-MYH7. Characterizing the coding region of canine TGM1 is a first step in examining the role of this enzyme in normal and defective cornification in the dog.

Cloning, sequence analysis and radiation hybrid mapping of a mammalian KRT2p gene

We report here on the cloning, characterization and radiation hybrid mapping of the canine basic keratin gene KRT2p. The gene spans 8.3 kb, consists of nine exons and eight introns, and is characterized by the typical features of both basic keratins and keratins in general, including glycine-rich head and tail domains, which flank an alpha-helical rod domain of approximately 310 amino acids. Comparisons of sequence and structure reveal that canine KRT2p is strikingly similar to human KRT2p. Alignment of the predicted amino acid sequences for human and dog reveals greater than 80% identity. In the rod domain, the amino acid identity exceeds 90%. We note, however, that canine KRT2p encodes a protein 21 residues longer than human K2p due to the insertion of a glycine repeat motif, GG(G)X, in the head and tail domains of the canine gene. This is the first report of the nearly complete genome sequence for KRT2p of any organism. Radiation hybrid mapping of canine KRT2p to chromosome 27 of the dog is also reported.

Analysis of the chromosome sequence of the legume symbiont Sinorhizobium meliloti strain 1021

Sinorhizobium meliloti is an alpha-proteobacterium that forms agronomically important N(2)-fixing root nodules in legumes. We report here the complete sequence of the largest constituent of its genome, a 62.7% GC-rich 3,654,135-bp circular chromosome. Annotation allowed assignment of a function to 59% of the 3,341 predicted protein-coding ORFs, the rest exhibiting partial, weak, or no similarity with any known sequence. Unexpectedly, the level of reiteration within this replicon is low, with only two genes duplicated with more than 90% nucleotide sequence identity, transposon elements accounting for 2.2% of the sequence, and a few hundred short repeated palindromic motifs (RIME1, RIME2, and C) widespread over the chromosome. Three regions with a significantly lower GC content are most likely of external origin. Detailed annotation revealed that this replicon contains all housekeeping genes except two essential genes that are located on pSymB. Amino acid/peptide transport and degradation and sugar metabolism appear as two major features of the S. meliloti chromosome. The presence in this replicon of a large number of nucleotide cyclases with a peculiar structure, as well as of genes homologous to virulence determinants of animal and plant pathogens, opens perspectives in the study of this bacterium both as a free-living soil microorganism and as a plant symbiont.

Nucleotide sequence and predicted functions of the entire Sinorhizobium meliloti pSymA megaplasmid

The symbiotic nitrogen-fixing soil bacterium Sinorhizobium meliloti contains three replicons: pSymA, pSymB, and the chromosome. We report here the complete 1,354,226-nt sequence of pSymA. In addition to a large fraction of the genes known to be specifically involved in symbiosis, pSymA contains genes likely to be involved in nitrogen and carbon metabolism, transport, stress, and resistance responses, and other functions that give S. meliloti an advantage in its specialized niche.

The composite genome of the legume symbiont Sinorhizobium meliloti

The scarcity of usable nitrogen frequently limits plant growth. A tight metabolic association with rhizobial bacteria allows legumes to obtain nitrogen compounds by bacterial reduction of dinitrogen (N2) to ammonium (NH4+). We present here the annotated DNA sequence of the alpha-proteobacterium Sinorhizobium meliloti, the symbiont of alfalfa. The tripartite 6.7-megabase (Mb) genome comprises a 3.65-Mb chromosome, and 1.35-Mb pSymA and 1.68-Mb pSymB megaplasmids. Genome sequence analysis indicates that all three elements contribute, in varying degrees, to symbiosis and reveals how this genome may have emerged during evolution. The genome sequence will be useful in understanding the dynamics of interkingdom associations and of life in soil environments.

Ribosomal protein gene cluster analysis in eubacterium genomics: homology between Sinorhizobium meliloti strain 1021 and Bacillus subtilis

The first whole genome sequence of a symbiotic soil bacterium, Sinorhizobium meliloti (formely named Rhizobium meliloti) strain 1021, is due in 2001. As an active participant in the European and North American consortium that has completed this work, our group has sequenced a region on the chromosome containing clusters rpoBC, str, S10, spc and alpha corresponding to 30 protein genes. The structural organization and function of these genes were compared with those of orthologs in another 15 complete eubacterial genomes available in databases. This study, involving the DNA and amino acid sequences as well as the organization of the whole region (gene order, cluster order, etc.), has shown that the phylogenetic tree resulting from a comparison of the amino acid sequence is rather similar to that derived from 16S rRNA sequence data. However, the tree achieved by aligning DNA sequences groups the organisms with a high GC content (>60% GC), while that based on a comparison of gene cluster orientation and organization reveals a greater level of correspondence between the alpha-proteobacteria S.meliloti and the firmicute Bacillus subtilis.

Sequencing the Sinorhizobium meliloti genome

The Sinorhizobium meliloti genome consists of three replicons. This bacterium forms an intricate symbiotic relationship with the roots of certain legumes and is considered as an agriculturally important nitrogen-fixer. A consortium of 6 European laboratories was organized to sequence its single chromosome (3.7 Mb), whereas the other two elements (pSyma 1.4 Mb and pSymb 1.7 Mb) will be sequenced by other groups.

Characterization of a minimal screening set of 172 microsatellite markers for genome-wide screens of the canine genome

We have characterized a subset of 172 microsatellite markers from the canine map, termed 'Minimal Screening Set 1' (Canine MSS-1), which we propose be used for initial genome-wide genetic linkage studies. Three hierarchical criteria were used to select markers from the current meiotic linkage and radiation hybrid maps for MSS-1. Markers were selected that (1) provided as complete coverage as possible of the canine genome, (2) were highly informative, and (3) have been ordered in linkage groups with a high degree of statistical support. This resulting screening set spans all reported meiotic linkage and RH groups, leaving only 10 known gaps > or = 20 cM. The average polymorphic information content (PIC) value of markers tested is 0.74. Coverage estimates suggest 42% of the genome is within 5 cM of at least one marker in the minimal screening set, 77% of the genome is within 10 cM. This minimal mapping set therefore provides an efficient and cost effective way to begin screening pedigrees of interest for genetic linkage.

Transcriptional analysis of the 69-kb sequence centromeric to HLA-J: a dense and complex structure of five genes

Performed within the framework of the sequencing of the 356-kb MHC class I distal region, systematic bioinformatic annotation and preliminary experiments conducted on the whole sequence indicate a high level and a complex pattern of expression. In this paper, we analyze a particular stretch of 69 kb centromeric to the HLA-J gene, in which we identify 21 different mRNAs mainly expressed in testis, and characterize five different transcription units, HZFw, HZFc, HCGV, HTEX6, and HTEX4. These tightly linked genes form a cluster conserved between human and mouse and displaying a high gene density of about one every 14 kb. Alternative splicing processes are observed for all the genes, together with an alternative polyadenylation event for gene HTEX4, sense/antisense mRNA overlaps for HZFw and HZFc, for HZFw and HCGV at their 3' end, and for HTEX6 and HTEX4 at their 5' end. This complex genomic structure suggests a mechanism of coregulation by cis-interaction in gene expression.

POL32, a subunit of the Saccharomyces cerevisiae DNA polymerase delta, defines a link between DNA replication and the mutagenic bypass repair pathway

Pol32 is a subunit of Saccharomyces cerevisiae DNA polymerase delta required in DNA replication and repair. To gain insight into the function of Pol32 and to determine in which repair pathway POL32 may be involved, we extended the analysis of the pol32delta mutant with respect to UV and methylation sensitivity, UV-induced mutagenesis; and we performed an epistasis analysis of UV sensitivity by combining the pol32delta with mutations in several genes for postreplication repair (RA D6 group), nucleotide excision repair (RAD3 group) and recombinational repair (RAD52 group). These studies showed that pol32delta is deficient in UV-induced mutagenesis and place POL32 in the error-prone RAD6/ REV3 pathway. We also found that the increase in the CAN1 spontaneous forward mutation of different rad mutators relies entirely or partially on a functional POL32 gene. Moreover, in a two-hybrid screen, we observed that Pol32 interacts with Srs2, a DNA helicase required for DNA replication and mutagenesis. Simultaneous deletion of POL32 and SRS2 dramatically decreases cellular viability at 15 degrees C and greatly increases cellular sensitivity to hydroxyurea at the permissive temperature. Based on these findings, we propose that POL32 defines a link between the DNA polymerase and helicase activities, and plays a role in the mutagenic bypass repair pathway.

High-resolution physical map of the pSymb megaplasmid and comparison of the three replicons of Sinorhizobium meliloti strain 1021

A high-resolution physical map of the larger megaplasmid (pSymb) of Sinorhizobium meliloti strain 1021 has been constructed by using BAC libraries and an original two-step PCR screening method. This method, previously used to map both the chromosome and the smaller megaplasmid (pSyma), allowed us to position over the genome a total of 842 markers with an average density of one marker every 8.3 kb. In addition, we used BLASTX and PRODOM analysis to predict a function for a number of STSs. This work led to the discovery of several interesting loci and to a comparison of the genetic information carried by each replicon. The two main results emerging from this study are (i) a biased distribution of housekeeping genes, mainly detected on chromosome, and (ii) the presence of an unexpected number of transporters, mainly belonging to the ABC superfamily. These are broadly distributed across the whole genome, but particularly found on pSymb.

Identification and characterization of a set of 100 tri- and dinucleotide microsatellites in the canine genome

A set of 100 canine microsatellite markers--83 dinucleotides and 17 trinucleotides--is reported. A study of their frequency in the dog genome showed that, while the frequency of the CA repeats is one (CA)n every 47 kb, the 10 trinucleotidic frequencies vary from one every 117 kb (AGG)n to one every 875 kb (AGT)n. Polymorphism analysis performed on 16 unrelated mongrel dogs showed that 80% of dinucleotides are polymorphic, while only 30% of the trinucleotides are so. Of this set of 100 markers, 56 have been mapped on the RHDF5000 dog/hamster whole genome radiation hybrid panel. Moreover, through systematic BLAST analogy searches of the microsatellite-containing clone sequence, three new dog genes could be identified, based on their human ortholog. All of the markers presented may prove useful in physical mapping methods, and polymorphic microsatellites in genetic linkage studies or parentage controls in dog.

A 356-Kb sequence of the subtelomeric part of the MHC Class I region

The subtelomeric part of the MHC Class I region contains 11 of the 21 genes described on chromosome 6 at position 6p21.3. The general organization of those and other genes resident in the region was revealed by determining a 356,376 bp sequence. Potential exons for new genes were identified by computer analysis and a large number of ESTs were selected by testing the sequence by the BLAST algorithm against the GenBank nonredundant and EST databases. Most of the ESTs are clustered in two regions. In contrast, the whole HLA-gene region is crammed with LINE and SINE repeats, fragments of genes and microsatellites, which tends to hinder the identification of new genes.

Using the fluorogenic 5' nuclease assay for high-throughput detection of (CA)n repeats in radiation hybrid mapping

Here, the power of the 5' nuclease assay to detect PCR products containing (CA)n repeats was compared with that of the classical electrophoretic analysis. This assay, which relies on the use of a unique (CA)10 energy transfer-labeled probe and the 5' nuclease activity of Taq DNA polymerase, was used to construct a dog radiation hybrid map consisting of microsatellite markers. Data from over 7000 PCRs were analyzed in parallel by the fluorogenic assay and the conventional ethidium bromide-stained, agarose gel-based assay. We show that the fluorogenic assay provides a sensitive, reliable and specific method for detecting (CA)n amplimers. Moreover, as no processing is required after the PCR, the risk of carryover contamination and the time required for sample analysis are greatly reduced. All radiation hyrid (RH) assays can be performed using a single PCR protocol, and a standard analysis method has been developed that enables numerically automated data processing. On the whole, using this strategy greatly enhanced the rapidity, throughput and accuracy of the RH mapping of microsatellite markers.

From sequence to chromosome: the tip of the X chromosome of D. melanogaster

One of the rewards of having a Drosophila melanogaster whole-genome sequence will be the potential to understand the molecular bases for structural features of chromosomes that have been a long-standing puzzle. Analysis of 2.6 megabases of sequence from the tip of the X chromosome of Drosophila identifies 273 genes. Cloned DNAs from the characteristic bulbous structure at the tip of the X chromosome in the region of the broad complex display an unusual pattern of in situ hybridization. Sequence analysis revealed that this region comprises 154 kilobases of DNA flanked by 1.2-kilobases of inverted repeats, each composed of a 350-base pair satellite related element. Thus, some aspects of chromosome structure appear to be revealed directly within the DNA sequence itself.

Canine genetics comes of age

The dog, as human's favored companion, is unique among animal species in providing new insights into human genetic disease. In this review, we will discuss both the breed and the population structure of dogs and why that makes canines amenable to genetic studies. We will review the current state of the map and discuss the particular disease states in which canines stand to make the greatest contribution to medical genetics.

High-resolution physical map of the Sinorhizobium meliloti 1021 pSyma megaplasmid

To facilitate sequencing of the Sinorhizobium meliloti 1021 pSyma megaplasmid, a high-resolution map was constructed by ordering 113 overlapping bacterial artificial chromosome clones with 192 markers. The 157 anonymous sequence tagged site markers (81,072 bases) reveal hypothetical functions encoded by the replicon.

An integrated linkage-radiation hybrid map of the canine genome

Purebred dogs are a unique resource for dissecting the molecular basis of simple and complex genetic diseases and traits. As a result of strong selection for physical and behavioral characteristics among the 300 established breeds, modern dogs are characterized by high levels of interbreed variation, complemented by significant intrabreed homogeneity. A high-resolution map of the canine genome is necessary to exploit the mapping power of this unusual resource. We describe here the integration of an expanded canine radiation hybrid map, comprised of 600 markers, with the latest linkage map of 341 markers, to generate a map of 724 markers-the densest map of the canine genome described to date. Through the inclusion of 217 markers on both the linkage and RH maps, the 77 RH groups are reduced to 44 syntenic groups, thus providing comprehensive coverage of most of the canine genome.

Construction and optimization of a dog whole-genome radiation hybrid panel

A dog whole-genome radiation hybrid (WGRH) panel including 126 clones was constructed by fusing dog fibroblasts irradiated at 5000 rads with thymidine kinase-deficient hamster cells. The average retention frequency of the panel designated as RHDF5000 is 21%, and its resolution power is estimated at 600 kb. The data provided by typing 400 markers were used to estimate linkage power changes subsequent to panel reduction. These changes were analyzed by recomputing typing data from five reduced panels. From these simulations, the parameters allowing investigation of the evolution of the linkage power in the course of panel reduction were determined. Guidelines for constructing a WGRH panel are proposed.

A high-density physical map of Sinorhizobium meliloti 1021 chromosome derived from bacterial artificial chromosome library

As part of the European Sinorhizobium meliloti (strain 1021) chromosome sequencing project, four genomic bacterial artificial chromosome (BAC) libraries have been constructed, one of which was mainly used for chromosome mapping. This library consists of 1,824 clones with an average insert size of 80 kilobases and represents approximately 20-fold total genome coverage [6.8 megabases (Mbs)]. PCR screening of 384 BAC clones with 447 chromosomal markers (PCR primer pairs), consisting of 73 markers representing 118 genes (40 individual genes and 78 genes clustered in 23 operons), two markers from the rrn operon (three loci), four markers from insertion sequences (approximately 16 loci) and 368 sequence-tagged sites allowed the identification of 252 chromosomal BAC clones and the construction of a high-density physical map of the whole 3.7-Mb chromosome of S. meliloti. An average of 5.5 overlapping and colinear BAC clones per marker, correlated with a low rate of deleted or rearranged clones (0.8%) indicate a solid BAC contigation and a correct mapping. Systematic BLASTX analysis of sequence-tagged site marker sequences allowed prediction of a biological function for a number of putative ORFs. Results are available at. This map, whose resolution averages one marker every 9 kilobases, should provide a valuable tool for further sequencing, functional analysis, and positional cloning.

Characterization of 463 type I markers suitable for dog genome mapping

In total, 463 canine gene markers were identified and characterized to serve as reagents in canine genome map projects. These markers are distributed over 221 canine gene markers, 139 TOASTs (Traced Orthologous Sequence Tags), 27 canine TOASTs, and 76 huESTs (human Expressed Sequence Tags). Out of 310 canine gene markers, 59%-84% were successfully amplified on dog DNA, the highest rates of success being observed when the exon/intron structure is known. Concerning TOASTs and human ESTs, of the 225 and 300 markers analyzed, 62% and 25% respectively were able to produce a dog positive amplification. As part of an ongoing project to map the canine genome using a dog/hamster radiation hybrid panel, these markers were tested for their specificity on dog versus hamster DNA. Thus 61%, 21%, and 12% of dog gene markers, TOASTs, and huESTs met the criteria required for radiation hybrid mapping, respectively. All of these 463 canine gene markers, however, are available and will be of value to any other mapping strategies.

Microsatellite analysis using a two-step procedure for fluorescence labeling of PCR products

A method for fluorescent labeling of PCR products has been developed. This method consists in a two-step procedure in which a first exponential classical PCR is followed by a "linear amplification". This second step relies on incorporation of fluorescent dNTP (dUTP or dCTP) in order to label the product on only one strand. The products can be applied without prior purification directly to a gel on a fluorescence-based automated DNA sequencer, for length and allele determination. The reliability of the results equals those of the classical 32P or fluorescent primer labeling methods, and the method is definitely less costly. Since the interpretation of the results is easier than with the method consisting in a fluorescent dNTP uptake in both strands in a single PCR, the present strategy should prove useful in mapping projects requiring analysis of a large number of microsatellites.